Pipes are typically produced from a metal block either by fitting a mandrel through the block and then rolling it out, or by welding a metal sheet that has previously been formed into the desired tubular shape. When pipes of this type are employed, in particular, as pipeline elements for transporting liquid or gaseous media under high pressure, a high priority is placed on the quality and shape accuracy of the pipes.
The quality-specific requirements cover not only the surface quality and the slightest possible deviations from the previously specified wall thickness over the entire length of the pipe, but also the three-dimensional shape of the entire pipe at multiple locations on the two-dimensional shape of the pipe cross-section.
Especially strict requirements must be met in terms of the shape of the pipe over its entire length especially in the case of pipes for pipelines that are laid on the ocean floor and are thus subject at the place of use not only to the specified inside pressures but also to high external pressures. Even small deviations from the desired roundness of the pipe cross-section, known as ovalty, can result in local indentations in the pipe or in problems in welding two pipes together.
The pipe manufacturer must therefore typically ensure that the roundness of the pipe lies within the specified tolerances over its entire length, and thus even far removed from the pipe ends. For this reason, mechanical measuring elements such as calipers or measurement clamps are typically used at the pipe ends to measure the shape of the pipe. The diameter of the pipe is then typically measured at three previously determined measurement points in order to thereby derive information about the roundness or ovalty of the entire pipe between the ends.
However, it is almost impossible, or possible only by expensive means, to determine the complete shape of the pipe over its full length. In addition, when such measurements are made the pipes are lying either in storage or on a conveying roller bed on a limited number of supports that are not always in the same position or orientation, with the result that both any bending of the pipe over its length as well as deformations in the shape of the pipe due to its own weight have a considerable effect on each measurement.
A need therefore exists for a standardized measurement method for determining the contour and shape of these types of pipe, which method is not yet available. There is similarly a need to be able to perform the measurements required for measuring quality and ensuring quality as much as possible automatically, and preferably also in a standardized fashion.